Conventionally, a cutting tool such as a face mill and an end mill, particularly an economically excellent throw-away type cutting tool in which a cutting insert is installed in a holder for use is used in many cases.
For example, Patent Document 1 discloses a cutting insert in which a rake face makes a positive rake angle relative to a main cutting edge in a state that the cutting insert is installed in a holder and the main cutting edge is divided by a groove portion extending substantially perpendicular to the main cutting edge in a top view. Such a cutting insert discharges a great deal of chip and is used mainly for heavy cutting with large cutting resistance at the time of cutting. In this case, since the main cutting edge is formed by a plurality of separate main cutting edges divided by the groove portion, the chip finely divided in the width direction is discharged. In such a way, since the discharged chip is finely divided in the width direction, it is possible to reduce the cutting resistance at the time of cutting. As a result, it is possible to reduce chatter vibration during the work.
However, in the cutting insert described in Patent Document 1, the groove portion extends substantially perpendicular to the main cutting edge in a top view. Therefore, in a case where the cutting insert is used while being attached to the holder so that the main cutting edge is inclined relative to a holder axis as in the face mill and the like, a non-cutting portion (an uncut portion) passing through the groove portion at the time of cutting is brought in interference with the cutting insert. Therefore, friction resistance is generated, and hence there is a problem that the cutting resistance at the time of cutting is increased.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 07-299636